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Registered Member #1727
Joined: Wed Oct 01 2008, 02:38PM
Location:
Posts: 5
Hello, im building this power supply:
In the simulation with PSpice the circuit works well, but when i build it i have this problem:
With out charge i set the output voltage at 100V (voltage setting input at 1.25V). When i charge the circuit with 5K, the output voltage down to 95V(aprox).
Then, with out charge i set the output voltage at 300V (voltage setting input at 3.75V). When i charge the circuit with 5K, the output voltage down to 275V (aprox).
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I suggest checking for oscillations with a scope.
FWIW, I built a similar power supply years ago and it's been working fine. (There is one mistake in that schematic: the foldback current limiting won't work.)
Registered Member #1727
Joined: Wed Oct 01 2008, 02:38PM
Location:
Posts: 5
Thank you for your response! In the EDA forum a user suggested a series capacitor (about 1-10nF) for R4. Because the actual realimentation is a P type with low gain, with the capacitor, will be a PI type and work better.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You're making your own curve tracer? Cool If so, bear in mind that the PI controller will have a longer settling time: you'll need to allow some time after each change of voltage.
Registered Member #1727
Joined: Wed Oct 01 2008, 02:38PM
Location:
Posts: 5
Yes, i'm making a USB curve tracer. At the moment, I'm working in the SMPS that provide 400V for the plate and the screen and -100 for the grid. And working with these linear power supply.
I put a 2.2n capacitor and the power supply works good! . But i have another problem. With 0V input, i set the LM317 bias for 0V output. After, i increment a little bit the control voltage input and i have 18V output, then i increment another little bit the control voltage and the output voltage down to 10V, then i increment the voltage control input and i have a normal operation.
I have something like this (the voltages are approximated):
Registered Member #1727
Joined: Wed Oct 01 2008, 02:38PM
Location:
Posts: 5
Sorry, the problem is not the power supply. I generate the voltage control with a resistor divider voltage, apparently the potentiometer is not working well. I measured (again, with a more precise tester range) the voltage control again, and the same curve is repeated in the input control voltage. I will buy another potentiometer and post results.
Thank you for the help .
PS: The current output of the power supply is about 200 mA. I'm not sure if parallelize two MOSFET for improve the power dissipation may be a problem...
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High voltage linear power supply (0-400V)
If so, bear in mind that the PI controller will have a longer settling time: you'll need to allow some time after each change of voltage.
